Ablative surgical interventions for PD involve stereotactic lesions in the globus pal-lidus, thalamus, or subthalamic nucleus to reduce motor symptoms. Cognitive and emotional outcomes after ablative procedures for PD in the 1950s and 1960s are sparsely documented. Wilkinson and Tröster (142) pointed out that outcomes from early and more recent studies are difficult to compare for a variety of reasons. In general, however, modern studies reveal that ablative procedures such as pallidotomy, thalamotomy, and subthalamotomy (especially unilateral) are relatively safe from a cognitive perspective.
With regard to unilateral pallidotomy, declines in verbal fluency performance have been reported in approximately 75% of outcome studies that included a measure of verbal fluency (62,143-145). Postoperative decrements on measures of attention, memory, and executive functions (typically mild and transient) have been reported more occasionally, and significant cognitive complications even more rarely (146,147). Preexisting cognitive impairment, advanced age, and dominant hemisphere surgery have been proposed to increase the risk for postoperative cognitive decline.
Few formal neuropsychological studies of bilateral pallidotomy have been undertaken, despite the observation that the most frequent adverse events among such patients are declines in speech and cognition (147). Despite their small number, these studies yield inconsistent findings. Some suggest that cognitive declines after bilateral pallidotomy may be limited in scope and severity (148,149), or that some gains in memory might be observed (150), but others report marked morbidity (151,152).
Although early studies examining outcomes after thalamotomy reported decrements in language and memory with regularity (113), modern thalamotomy is associated with minimal risk of cognitive morbidity (153,154). Initial reports of the apparent cognitive safety of subthalamotomy (155,156) remain to be confirmed by larger, controlled studies.
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